Repositório Comunidade: DQhttp://hdl.handle.net/10362/421
DQTue, 31 Mar 2015 18:17:37 GMT2015-03-31T18:17:37ZRepositório Comunidade: DQhttp://run.unl.pt:80/retrieve/1351/dq1.gifhttp://hdl.handle.net/10362/421
Bioremediation and CO2 scavenging using molybdenum-containing enzymeshttp://hdl.handle.net/10362/14581
Título: Bioremediation and CO2 scavenging using molybdenum-containing enzymes
Autor: Fonseca, Luís Filipe Madureira
Resumo: Carbon dioxide valorization, will not only help to relieve the greenhouse effect but might also allow us to transform it in value-added chemicals that will help overcoming the energy crisis. To accomplish this goal, more research that focus on sequestering CO2 and endeavors through a carbon-neutral or carbon-negative strategy is needed in order to handle with the dwindling fossil fuel supplies and their environmental impact. Formate dehydrogenases are a promising means of turning CO2 into a biofuel that will allow for a reduction of greenhouse gas emissions and for a significant change to the economic paramount. The main objective of this work was to assess whether a NAD+-independent molybdenum-containing formate dehydrogenase is able to catalyze the reduction of CO2 to formate. To achieve this, a molybdenum-containing formate dehydrogenase was isolated from the sulfate reducing bacteria Desulfovibrio desulfuricans ATCC 27774. Growth conditions were found that allowed for a greater cellular mass recovery and formate dehydrogenase expression. After growth trials, kinetic assays for formate oxidation and CO2 reduction were performed and kinetic parameters determined. For the formate oxidation reaction, a KM of 49 μM and a turnover constant of 146 s-1 were determined. These kinetic parameters are in agreement with those determined by Mota, et al. (2011). Finally, we found that this molybdenum-containing enzyme was able to catalyze the reduction of CO2 to formate with a turnover constant of 4.6 s-1 and a KM of 13 μM. For the first time a NAD+-independent molybdenum-containing formate dehydrogenase was found to catalyze CO2 reduction, allowing its use as a biocatalyst in energetically efficient CO2 fixation processes that can be directed towards bioremediation or as an alternative and renewable energy source. Characterizing these enzymes may lead to the development of more efficient synthetic catalysts, make them readily available and more suited for practical applications.Wed, 01 Oct 2014 00:00:00 GMThttp://hdl.handle.net/10362/145812014-10-01T00:00:00ZCharacterization of novel heme-containing sensor proteins from Geobacter sulfurreducenshttp://hdl.handle.net/10362/14390
Título: Characterization of novel heme-containing sensor proteins from Geobacter sulfurreducens
Autor: Silva, Marta Alexandra Fernandes
Resumo: The focus of this Thesis was the study of the sensor domains of two heme-containing methyl-accepting chemotaxis proteins (MCP) from Geobacter sulfurreducens: GSU0582 and GSU0935. These domains contain one c-type heme, form swapped dimers with a PAS-like fold and are the first examples of a new class of heme sensors.
NMR spectroscopy was used to assign the heme and polypeptide signals in both sensors, as a first step to probe conformational changes in the vicinity of the hemes. However, the presence of two conformations in solution impaired the confident assignment of the polypeptide signals.
To understand how conformational changes and swapped dimerization mechanism can effectively modulate the function of the two sensor domains and their signal transduction process, the sensor domains folding and stability were studied by circular dichroism and UV-visible spectroscopy. The results showed differences in the thermodynamic stability of the sensors, with GSU0582 displaying higher structural stability. These studies also demonstrated that the heme moiety undergoes conformational changes matching those occurring at the global protein structure and that the content of intrinsically disordered segments within these proteins (25% for GSU0935; 13% for GSU0582) correlates with the stability differences observed.
The thermodynamic and kinetic properties of the sensor domains were determined at different pH and ionic strength by visible spectroscopy and stopped-flow techniques. Despite the remarkably similar spectroscopic and structural features of the two sensor domains, the results showed that their properties are quite distinct. Sensor domain GSU0935 displayed more negative reduction potentials and smaller reduction rate constants, which were more affected by pH and ionic strength. The available structures were used to rationalize these differences.
Overall, the results described in this Thesis indicate that the two G. sulfurreducens MCP sensor domains are designed to function in different working potential ranges, allowing this bacterium to trigger an adequate cellular response in distinct anoxic subsurface environments.Wed, 01 Oct 2014 00:00:00 GMThttp://hdl.handle.net/10362/143902014-10-01T00:00:00ZNovel ready-to-eat mango product using gellan gum as gelling agent: physico-chemical, microbial and sensory characteristicshttp://hdl.handle.net/10362/14388
Título: Novel ready-to-eat mango product using gellan gum as gelling agent: physico-chemical, microbial and sensory characteristics
Autor: Danalache, Florina Andreea
Resumo: The development of novel food products designed to maximise both the health benefits and enjoyment of the consumer’s eating experience is an important area of research nowadays. Fruits and vegetables are also increasingly recognized as important components of a healthy diet. Within this context, the work in this thesis aimed the development of a novel convenient food product – fresh like mango bars - based on mango (Mangifera indica L) and gellan gum, designed to have sensory quality similar to that of fresh mango, to be of easy consumption and to have an extended shelf-life.
The influence of gellan concentration and of the ratio of L (low acyl)/H (high acyl) gellan on the rheological and microstructural properties of mango/gellan gels was studied. This allowed optimising the concentration of gellan. The effect of the L/H ratio on texture, microstructure, syneresis and sensory acceptance was evaluated. Results separated bars into two sets: one showing a higher hardness and lower syneresis (only L gellan and L/H in the ratios of 75/25 and 50/50); and the other with bars having a higher proportion of H, with a softer structure with higher cohesiveness and syneresis (L/H25/75 and only H gellan). Through sensory analysis the bar with L/H 25/75 was identified as the preferred one.
An edible coating was developed to improve the characteristics of the product. Its optimization was performed by the use of experimental design and mathematical modelling. Results showed that the coating improved appearance and firmness of bars, and reduced syneresis and volatiles loss during storage.
Thermal and high hydrostatic pressure preservation treatments were applied on packaged products. Both treatments had similar performance considering microbial content and aroma release. Thermally treated bars were stored at 5 °C during 21 days, without changing significantly their texture, colour, microbial loading and sensory attributes.
Overall results show that the process allows producing a stable ready-to-eat mango bar product appreciated by the sensory panellists.
Descrição: Este trabalho foi efectuado com o apoio da Universidade de Lisboa, Instituto Superior
de Agronomia com o Centro de Engenharia dos Biossistemas (CEERMon, 01 Dec 2014 00:00:00 GMThttp://hdl.handle.net/10362/143882014-12-01T00:00:00ZThe effect of key process operational conditions on enhanced biological phosphorus removal from wastewaterhttp://hdl.handle.net/10362/14295
Título: The effect of key process operational conditions on enhanced biological phosphorus removal from wastewater
Autor: Carvalheira, Mónica Isabel Gonçalves
Resumo: Enhanced biological phosphorus removal (EBPR) is the most economic and sustainable option used in wastewater treatment plants (WWTPs) for phosphorus removal. In this process it is important to control the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), since EBPR deterioration or failure can be related with the proliferation of GAOs over PAOs. This thesis is focused on the effect of operational conditions (volatile fatty acid (VFA) composition, dissolved oxygen (DO) concentration and organic carbon loading) on PAO and GAO metabolism. The knowledge about the effect of these operational conditions on EBPR metabolism is very important, since they represent key factors that impact WWTPs performance and sustainability. Substrate competition between the anaerobic uptake of acetate and propionate (the main VFAs present in WWTPs) was shown in this work to be a relevant factor affecting PAO metabolism, and a metabolic model was developed that successfully describes this effect. Interestingly, the aerobic metabolism of PAOs was not affected by different VFA compositions, since the aerobic kinetic parameters for phosphorus uptake, polyhydroxyalkanoates (PHAs) degradation and glycogen production were relatively independent of acetate or propionate concentration. This is very relevant for WWTPs, since it will simplify the calibration procedure for metabolic models, facilitating their use for full-scale systems. The DO concentration and aerobic hydraulic retention time (HRT) affected the PAO-GAO competition, where low DO levels or lower aerobic HRT was more favourable for PAOs than GAOs. Indeed, the oxygen affinity coefficient was significantly higher for GAOs than PAOs, showing that PAOs were far superior at scavenging for the often limited oxygen levels in WWTPs. The operation of WWTPs with low aeration is of high importance for full-scale systems, since it decreases the energetic costs and can potentially improve WWTP sustainability. Extended periods of low organic carbon load, which are the most common conditions that exist in full-scale WWTPs, also had an impact on PAO and GAO activity. GAOs exhibited a substantially higher biomass decay rate as compared to PAOs under these conditions, which revealed a higher survival capacity for PAOs, representing an advantage for PAOs in EBPR processes. This superior survival capacity of PAOs under conditions more closely resembling a full-scale environment was linked with their ability to maintain a residual level of PHA reserves for longer than GAOs, providing them with an effective energy source for aerobic maintenance processes. Overall, this work shows that each of these key operational conditions play an important role in the PAO-GAO competition and should be considered in WWTP models in order to improve EBPR processes.Mon, 01 Dec 2014 00:00:00 GMThttp://hdl.handle.net/10362/142952014-12-01T00:00:00Z